[Ovmsdev] Framework V3.1

Michael Balzer dexter at expeedo.de
Mon Jan 2 19:44:21 HKT 2017

Happy new year everyone :)

As you may have seen, I submitted a rework of the network framework

My goals were to a) eliminate hard coded delays as far as possible to
get faster command responses, b) more stable/reliable tickers and c)
higher frequency logging.

I've managed to achieve goals a & b. Commands are now processed in
around one second instead of three, and logging is now very stable, for
example GPS streaming will be very close to one entry every three seconds.

Higher frequency logging would be possible, but I've run into a hardware
issue with this: the modem (both 908 and 808 versions) runs into under
voltage problems if GPRS sends occur faster than once every three
seconds on average. This will even work when the GSM cell does not
change, but if the modem also needs to switch cells on the road, it
occasionally just powers down without warning. This may also happen when
the modem needs very high send power levels, i.e. if the next GSM tower
is far away.

The hardware design document says:
/"The transmitting burst will cause voltage drop and the power supply
must be able to provide sufficient current up to 2A. For the VBAT//
//input, a decoupling capacitor (low ESR) such as a 100 μF is strongly
...and the same problem could be solved here by adding a 10 µF buffer
capacitor to the power supply line:

So higher frequency logging may be possible when the modem does not need
to power up its own GPS circuit, i.e. when the car supplies GPS coordinates.

One GPS (speed) mark every three seconds is still sufficient, now it's

Btw, I also think I fixed the buffer overrun issue. I could reproduce
the bug by timing a command send to arrive at the module at the moment
the module starts a send itself. I then found some potential buffer
problems with this case in the net_poll() code. Since fixing them I had
no more events and can no longer trigger the bug with that command timing.

Please let me know if you run into new issues with this rework.


Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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